In a well known heated roller type fixing apparatus, two rollers--one of which is heated--are rotated in a condition of pressure contact with each other and a support (typically a sheet of paper) bearing an unfixed toner image on one face thereof is inserted between and for passage through the rollers. The first roller, which contacts the toner image borne on the support, is formed of a heat conductive metal such as brass and aluminum in the shape of a tube. A coating of a thermolubricity resistance material such as tetrafluoroethylene is provided on the tube periphery, and a heat source is disposed within its interior to thereby heat the roller's surface. The second roller, which is maintained for image fixing in pressing contact with the first roller, is formed of an elastic rubber such as silicon rubber.
During periods of nonoperation--i.e. when no toner image fixing is being performed--it is known to hold the two rollers in spaced apart relation so as to define a gap therebetween and to discontinue roller rotation (typically of the first or heated roller) until the next fixing operation. This may be done for a number of reasons, such as to enable the temperature of the surface of the first roller to be raised to a predetermined temperature within the shortest possible period of time, or to avoid permanent shape distortion of the elastic rubber of the second roller resulting from continued pressure contact with the first roller, or to protect against degradation of the roller rubber caused by high temperature, or to provide the ability to readily clear a paper jam occurring when the image support is transported and fixed.
Such prior art heated roller type fixing apparatus, however, suffer from an operating deficiency as shall now be described. In heated roller fixation, the support carrying thermoplasticizing toner is passed through the nip between the first or heated roller and the second roller in pressure contact therewith; the toner is fused by the heated roller and thereby fixed to the support. However, it is difficult to fix 100% of the toner to the support and additionally to keep the surface of the first roller entirely clean, and some of the unfixed toner residue and contamination from the support may become adhered to the first roller surface. As a countermeasure and in order to remove the toner residues and contamination which adhere to the first roller, a cleaning blade is provided in continuous contact with the first roller's heated surface.
In the course of repetitive copying operations, the toner residues accumulate at the contact position of the first roller with the cleaning blade, and these accumulated residues will solidify on the roller surface when copying operations are completed and the internal roller heat source is turned off. In this regard, it should be understood that in such conventional heated roller type fixing apparatus, no initiation of copying operations the first roller is heated and, following that, first roller rotation and pressing contact with the second roller commence almost simultaneously. A portion of the heated toner residues located on the first roller surface at the contact point with the cleaning blade may become separated from the cleaning blade and migrate to the surface of the pressing second roller from which they can adhere and be transferred to the rear or nonimage-bearing face of the passing support. This obviously has the serious and undesired effect, among others, of producing lowered copy quality.